Recently, I'm working on a C# project using SlimDX(Direct3D 9) to render 2D images in fullscreen mode. I'd like to use GDI window to do some settings. I've tried as followings, but it does not work, it will exit fullscreen mode when running to this code block. Does any one get some solutions with how to show a child form in fullscreen mode? Thanks. Bad English, hope you get my idea.